1. Field of the Invention
The present invention is a method and apparatus for improving the area available for reading and amplifying photodiode inputs to a multiplexer used with staring arrays.
2. Prior Art
Conventional staring arrays limit the photodiode input amplifier to the area available under each detector. Thus, if a detector array is on 60 micronsxc3x9760 microns spacing the available area on the multiplexing array it is interfaced to is 60xc3x9760 or 3600 square microns. FIG. 1 shows the logic and single amplifier input amplifiers for a 64xc3x9764 detector array multiplexer using 60 microns detector spacing. As the detector size is reduced, the available area on the multiplexer is reduced, and room for the input amplifier becomes unavailable. If for example a 40 micronsxc3x9740 microns detector spacing is chosen, the area available on the multiplexer becomes 1600 square microns, over 50 percent reduction of area.
The present invention modifies the input amplifier area by shunting a plurality of detector inputs into a common input amplifier at different times. The combination described in this invention is a four to one but any number of detectors could be combined depending on area needed and interconnecting methods. FIG. 3 gives the embodiment of the invention using a four to one combination as an example. With a four to one input to amplifier ratio, the available area of a 40 micronsxc3x9740 microns detector spacing is 40xc3x974xc3x9740 or 6400 square microns for four detectors and a common amplifier on the multiplexer array. This represents over a 50 percent improvement over the 60 micronsxc3x9760 microns area, for four detectors and four amplifiers. Some of this additional area is necessary for the combining electronics but allows the 40 microns detector spacing multiplexer to have the same amplifier as the 60 microns detector spacing multiplexer. FIG. 4 shows the logic and four to one combined input amplifier for a 128xc3x97128 detector array using 40 microns detector spacing. Thus, as the detectors become smaller, this invention permits the same amplifier to be used under the smaller areas by combining a plurality of detector outputs into the common amplifier.